1. Field of the Invention
The present invention relates to liquid crystalline polyvinylethers. More particularly, it relates to polymers which exhibit an optical anisotropic phase.
2 Description of the Prior Art
The work of Krigbaum et al (Mol. Cryst. Liq. Cryst., 1980, 62, 87) on main-chain and Finkelmann et al. (Makromol. Chem., 1978, 179, 273) and Ringsdorf et al. (Br. Polym. J., 1981, 13, 43) on side -chain polymer liquid crystals has generated interest in the potential of these systems for use in electrooptic devices.
Side-chain liquid crystalline polymers can be prepared by three different routes, i.e. addition polymerization, condensation polymerization and post-reactions of polymers (Finkelmann, Polymer Liquid Crystals, A. Ciferri, W. R., Krinbaum and Robert B. Meryer, Eds., Academic Press, New York (1982), Chapter 2). Among the three methods, the most convenient approach is to introduce the mesogenic unit beforehand into a reactive monomer capable of undergoing addition or chain-growth polymerization. However, for the most part, the side-chain liquid crystalline polymers prepared by chain-growth polymerization have been limited to polymethacrylates and polyacrylates (Finkelmann et al., Adv. Poly. Sci., 60/61, 99 (1984); Shibaev et al. Adv. Poly. Sci., 60/61, 173 (1984)) and polystyrene derivatives (Percec et al., Poly. Bull., 17, 347 (1984)), and these investigations were generally not concerned with the control of or the effect of molecular weight distribution on the properties of the liquid crystalline polymer. One example of such an investigation is the preparation of polymethacrylates by group-transfer polymerization (Kreuder et al., Makromol Chem. Rapid Commun., 7, 5 (1986)), but the molecular weight distribution range of these polymers was still quite broad (MwMn=1.2-1.8).
Higashimura and co-workers developed a living cationic polymerization procedure for vinyl ethers and propenyl ethers using an HI/I.sub.2 initiator system (Miyamoto et al., Macromolecules, 17, 265 (1984); Enoki et al., J. Poly. Sci., Poly. Chem. Ed., 24, 2261 (1986); Higashimura et al., J. Poly. Sci., Poly. Chem. Ed., 22, 3173 (1984); Higashimura et al., Macromolecules, 18, 611 (1985); Higashimura et al., Makromol. Chem. Suppl., 12, 153 (1985); Higashimura et al., U.S. Pat. No. 4,696,988). By this technique, in contrast to conventional cationic polymerization, even vinyl ethers containing polar groups polymerized in a polar solvent, such as CH.sub.2 Cl.sub.2 can form living polymers.
The cationic polymerization of 2-(4-biphenyloxy) ethyl vinyl ether and 2-(4'-methoxy-4-biphenyloxy) ethyl vinyl ether with conventional Lewis-acids has been reported (Rodriguez-Parada et al., J. Poly. Sci., Poly. Chem. Ed., 24, 1363 (1986)). However, these reactions yielded polymers with broad molecular weight distributions.